1. Field of the Invention
The present invention relates to improvements in a dither current power supply control method and apparatus, for applying an increase/decrease current to an inductive electric load for driving a reversible positioning actuator, against a static friction resistance acting on a driven body.
2. Description of the Related Art
For example, in a transmission control apparatus, a suspension control apparatus, and the like for a motor vehicle, a proportional solenoid valve for controlling a hydraulic cylinder, which is an actuator, is used. In order to control a position of a movable valve of the proportional solenoid valve, a dither current is supplied to a proportional solenoid coil, which is an inductive electric load. The proportional solenoid coil generates, against a static friction resistance acting on the movable valve and a spring force pressing the movable valve in one direction, a pressing force in the other direction to control the position of the movable valve.
Note that, in the inductive electric load, a response delay is generated in an increase/decrease in a load current based on a time constant Tx=L/R, which is a ratio of the inductance L to the load resistance R. When the rise time from a dither small current I1 to a dither large current I2 and the fall time from the dither large current I2 to the dither small current I1 are different from each other, a value of a dither medium current I0=(I1+I2)/2 of the dither large current I2 and the dither small current I1 and a value of a dither average current Ia acquired by dividing a time integral of the dither current by a dither amplitude cycle Td are different from each other.
Thus, in a case where such negative feedback control as to cause a target average current Iaa and a detected average current Idd to simply match each other is carried out without focusing on the dither medium current I0, consideration needs to be given to such a problem that homogeneous dither control cannot be carried out.
For example, in FIG. 1 of Japanese Patent Application Laid-open No. 2009-103300 (FIG. 1, FIG. 4, FIG. 6, Abstract, and paragraphs [0028], [0029], [0040] and [0045]), “CONTROL METHOD AND CONTROL DEVICE FOR PROPORTIONAL SOLENOID VALVE”, an MPU 3 (assumed to be) constructed by a microprocessor includes an opening amount corrector 6 for determining a target average current for a proportional solenoid valve 10, a dither signal generator 7, and a synthesizer 8. A constant current driver 5, which is (assumed to be) hardware externally connected to the MPU 3, carries out negative feedback control so that an instruction current acquired by converting an output of the synthesizer 8 into an analog signal by a D/A converter 4 and a drive current for the proportional solenoid valve 10 match each other. The negative feedback control includes first and second operational amplifiers 31 and 32, an adder 33, a buffer 34, a transistor 35, a current detector 36, and a differentiator/multiplier 37 illustrated in FIG. 6. The differentiator/multiplier 37 is configured to process an increase/decrease in the drive current at high speed.
However, as illustrated in FIG. 4(b) of Japanese Patent Application Laid-open No. 2009-103300, the increase/decrease in the drive current is a sinusoidal wave gradually increasing and decreasing, and in order to acquire a predetermined dither amplitude, a dither cycle may increase and a movable iron 14 (refer to FIG. 2) may be stuck by a static friction resistance.
Moreover, in FIG. 2 of Japanese Patent Application Laid-open No. 2014-197655 (FIG. 2 to FIG. 4, FIG. 15, and paragraphs [0010] to [0017] and [0040]), “CURRENT CONTROL DEVICE AND CURRENT CONTROL PROGRAM”, a current control device 10 (assumed to) including a microprocessor is configured to directly output a PWM signal Spwm to a drive circuit 50 for driving and switching a solenoid 95, is constructed by target setting means 20, duty ratio setting means 30, and PWM signal generation means 40 illustrated in FIG. 2. A technology of reducing a period from setting of a basic current value Ib by the target setting means 20 to updating of a duty ratio Rd by the PWM signal generation means 40 is disclosed.
In FIG. 4 of Japanese Patent Application Laid-open No. 2014-197655, in the target setting means 20, a basic setting unit determines the basic current value Ib, a dither average calculation unit 22 calculates a dither average current value Iave2 based on a detected excitation current signal Si, a subtraction unit 23 calculates a deviation value ΔI2, a correction unit 24 generates a proportional integral correction value for the basic current value Ib, a dither setting unit 25 sets a dither current Id, and an addition unit 26 calculates a target current value It.
Moreover, in FIG. 3 of Japanese Patent Application Laid-open No. 2014-197655, in the duty ratio setting means 30, a PWM average calculation unit 31 calculates a PWM average current value Iave1 based on the detected excitation current signal Si, a subtraction unit 32 calculates a deviation ΔI1, a feedback control unit 33 (description error of 34) calculates a duty ratio Rd/fb, a feedforward control unit 34 (description error of 33) calculates a duty ratio Rd/ff, and an addition unit 35 calculates a duty ratio Rd. The duty ratio setting means 30 is configured to adjust the duty ratio Rd of the PWM so that the target current It matches the PWM average current value Iave1.
Note that, in FIG. 2 of Japanese Patent Application Laid-open No. 2014-197655, the PWM signal generation means 40 generates the PWM signal Spwm, and outputs the PWM signal Spwm to the drive circuit, and the target current It is a value periodically changing at the dither cycle that is set to 10 times as long as the PWM cycle of the PWM signal Spwm.
The feedforward control unit 34 (description error of 33) in FIG. 3 of Japanese Patent Application Laid-open No. 2014-197655 is configured to apply the duty ratio Rd/ff so that a fundamental wave of the dither current becomes a triangular wave of FIG. 15 of Japanese Patent Application Laid-open No. 2014-197655. As a result of feedback control at the duty ratio Rd/fb by following the triangular wave, the triangular wave becomes a gentle waveform gradually increasing and decreasing, and in order to acquire a predetermined dither amplitude, the dither cycle may increase and a spool 942 (refer to FIG. 1 of Japanese Patent Application Laid-open No. 2014-197655) may be stuck due to the static friction resistance.
In “CONTROL METHOD AND CONTROL DEVICE FOR PROPORTIONAL SOLENOID VALVE” disclosed in Japanese Patent Application Laid-open No. 2009-103300, the dither current waveform is a sinusoidal wave gently changing, and when the control is carried out by exactly following the sinusoidal wave, the rise time and the fall time of the dither current match each other.
However, when the cycle of the sinusoidal wave is increased so that the current control may follow the sinusoidal wave, there is a problem in that a stationary state of the movable iron 14 occurs to generate the static friction resistance. Moreover, when the cycle of the sinusoidal wave is decreased, there is a problem in that the current control cannot follow and the rise time and the fall time of the dither current do not match each other.
Moreover, it is difficult to calculate a derivative, which is a degree of a change in a deviation signal between a pulsating instruction current and a pulsating detected current, based on the deviation signal, and there is a problem in that precise derivative control cannot be expected.
The same holds true for “CURRENT CONTROL DEVICE AND CURRENT CONTROL PROGRAM” disclosed in Japanese Patent Application Laid-open No. 2014-197655. The dither current waveform is a triangular wave gently changing, and when the control is carried out by exactly following the triangular wave, the rise time and the fall time of the dither current match each other.
However, when the cycle of the triangular wave is increased so that the current control may follow the triangular wave, there is a problem in that a stationary state of the spool 942 occurs to generate the static friction resistance. Moreover, when the cycle of the triangular wave is decreased, there is a problem in that the current control cannot follow and the rise time and the fall time of the dither current do not match each other.
Moreover, a calculation method for the PWM average current value Iave1 and a method for the feedforward control of FIG. 3 are not described at all, but a highly responsive microprocessor and a highly responsive AD converter are considered to be necessary.